1. Field of the Invention
The present invention relates to a transmitting and amplifying unit for a wireless communication device.
2. Description of the Related Art
In recent years, a wireless communication device for a mobile base station has been required to have a compact size, high output, and high reliability. The wireless communication device includes a transmitting and amplifying unit, a receiving unit, and a control unit. These units are mounted on a rack. In the transmitting and amplifying unit of the wireless communication device, many heating components such as power transistors are included especially in an amplifying portion of a microwave circuit. Accordingly, the transmitting and amplifying unit is required to have a radiating structure for efficiently radiating heat from these heating components.
Natural air cooling is adopted for radiation of heat from a transmitting device having a relatively small transmission output. However, in the case of a large transmission output as in a recent communication device, a large quantity of heat is generated and radiation by natural convection is therefore insufficient, so that a radiating structure employing forced air cooling becomes necessary. In general, a cooling fan and radiating fins are used for the radiation by forced air cooling. In the case of forced air cooling, a spacing between the radiating fins can be reduced as compared with the case of natural air cooling, and a sufficient radiating area can therefore be ensured. However, there is no difference in coefficient of heat transfer between forced air cooling and natural air cooling with the same material. Accordingly, although a large radiating area can be ensured in the case of forced air cooling, heat is radiated before it is transmitted over the radiating area. Thus, there is a limit to heat transfer, and the cooling is accordingly limited. As means for efficiently performing heat transfer, a heat pipe effective for heat transfer is known. However, the heat pipe loses a mounting density, so that it does not contribute to size reduction.
A known transmitting and amplifying unit includes a frame, a main amplifier unit mounted on the frame, a subamplifier unit mounted on the frame, a first radiating fin unit mounted on a heating portion of the main amplifier unit, a second radiating fin unit mounted on a heating portion of the subamplifier unit, and a cooling fan mounted at the rear end of the frame for forcibly air-cooling these heating portions. This conventional transmitting and amplifying unit has a plurality of printed wiring boards and a plurality of radiating fins, resulting in large weight and relatively complex structure. In the conventional transmitting and amplifying unit, each radiating fin has a large size, causing an increase in total weight of the transmitting and amplifying unit, thus hindering weight reduction.
To obtain an optimum radiation efficiency, a concentrated heating portion existing in the main amplifier unit must be efficiently cooled. However, there is a limit to the mounting portions of components due to the fact that electrical characteristics must be ensured. As a result, the conventional transmitting and amplifying unit does not have a radiating structure capable of efficiently cooling the concentrated heating portion. For example, each radiating fin is long in the longitudinal direction of the transmitting and amplifying unit, causing a large pressure loss. Further, the mounting position of the cooling fan is limited. Accordingly, cooling air drawn by the cooling fan cannot be mainly directed to the concentrated heating portion, and the radiation cannot be efficiently performed. Moreover, the conventional transmitting and amplifying unit employs many printed wiring boards and many connection cables for connecting the printed wiring boards. Further, the number of parts is large. As a result, the number of man-hours for assembly becomes large, causing a cost increase.